1. Field of the Invention
This invention relates to pipe swivel joints and in particular to such swivel joints which may be selectively placed in a swivel or a rigid connection mode.
2. Description of the Prior Art
Swivel joints and piping networks are widely used in petroleum pipe systems as well as in systems for the transfer of a wide variety of other fluid products. A pipe network associated with fluid loading arms requires swivel joints for proper positioning of the loading spout connectors. Swivel joints are also used in relatively inaccessible subsea flexible piping systems. Occasionally, flexibility is required to make a pipe connection after which a rigid sealed connection joint is desirable. When swivel joints in piping network are desirable, and particularly where the option to have a swiveling or a rigid joint desirable, a joint which can be set in either mode is of considerable advantage. Moreover, in a system where shutting off a pipe line means lost production, two such adjustable swivel joints may be connected in series at initial installation. With the spare swivel of the two in the rigid connection mode and the primary swivel in the swivel mode, a failure in the dynamic seal in the primary swivel will allow selection of the rigid connection mode in the primary swivel and release of the spare swivel from the rigid to the swivel mode. The changeover is accomplished without shut down in the line while reestablishing pipe system integrity.
Numerous swivels are currently available for piping networks, such as the various models of Chiksan swivel joints manufactured by FMC Corporation Petroleum Equipment Group headquartered in Houston, Texas. U.S. Pat. No. 3,142,498, issued to Press, discloses a swivel joint assembly having a flange portion and a connector portion. The connector portion has a widened ball bearing race formed on the inner surface thereof, and the flange portion has a relatively narrow ball bearing race formed on the outer surface thereof. The race in the connector portion overlies the race in the flange portion, and a number of ball bearings are placed within the races to allow relatively friction free rotation between the connector and flange portions. A coupling nut engages external threads on the flange portion and surrounds the connector portion. When the coupling nut is loose on the flange portion threads, the coupling is free to swivel and a dynamic seal prevents escape of fluid from the flow passing through the swivel joint. When the coupling is drawn up tightly on the flange portion threads, the connector portion is moved axially through the excess bearing end play afforded by the wide bearing race therein to contact a static seal and thereby provide a rigid connection joint which contains the fluid passing along the flow path through the joint.
Another swivel joint which may be selectively configured as a rigid connection or as a swiveling connection is disclosed in U.S. Pat. No. 3,752,507, issued to Maurer et al. In the Maurer et al disclosure a wash pipe assembly interconnects two sections of pipe. The assembly includes a centrally disposed wash pipe surrounded by two sleeves, and a packing in each of the sleeves to provide a seal about the outer periphery of the wash pipe and the inner surface of each sleeve. One of the sleeves is coupled to the free end of one pipe section and the other sleeve is connected to the free end of the opposing pipe section. Each of the sleeves is capable of being rotationally locked to the wash pipe and when both sleeves are locked a rigid connection between the two pipe sections results. Tandem packing arrangements in each sleeve provide a dynamic seal and a backup seal.
It is apparent that a swivel joint is highly desireable which may be selectively set to a swivel mode or a rigid connection mode, which has a static seal previously unused until the rigid connection mode is selected, and wherein axial adjustment to effect the rigid connection mode is unrestricted by bearing end play to thereby afford higher static pressure sealing capability.